Polyoxyalkylene polysiloxane mixed block polymers wherein the polysiloxane blocks are connected with the polyether blocks through SiC linkages are generally, from a technical point of view, prepared by an addition reaction between alkene polyethers, particularly allyl polyethers, and hydrogen siloxanes in the presence of platinum catalysts.
Such polyoxyalkylene polysiloxane mixed block polymers may correspond to the general formula ##STR1## wherein R.sup.1 =alkyl, usually methyl;
R.sup.2 =alkyl with 2 to 20 carbon atoms; PA1 R.sup.3 =(CH.sub.2).sub.3 O(C.sub.2 H.sub.4 O).sub.x (C.sub.3 H.sub.6 O).sub.y R.sup.4 ; PA1 R.sup.4 =hydrogen or alkyl with 1 to 4 carbon atoms; PA1 n=0 to 100; PA1 m=1 to 8, PA1 x=1 to 25; and PA1 y=0 to 25.
In the preparation of such polymers, an excess of allyl polyethers is employed and, in so doing and under the conditions of the addition reaction, a portion of the allyl polyethers is rearranged into the propenyl polyethers, which are not capable of entering the addition reaction.
Polyoxyalkylene polysiloxane mixed block polymers of the above indicated kind thus contain generally moieties of unreacted allyl polyethers and propenyl polyethers.
Such SiC linked polyoxyalkylene polysiloxane mixed block polymers are preferred as stabilizers in the production of polyurethane foams, as emulsifiers, separating agents, and as active ingredients in cosmetic products. However, they possess a more-or-less strongly noticeable distinct and unpleasant acrid odor which has a tendency to become stronger upon storage. This odor, of course, is an obstacle to the use of mixed block polymers of the indicated kind, and particularly when the polymers are to be used as active ingredients in cosmetic preparations.
Attempts have been made in the past to remove the odor forming components by blowing with inert gas or by treatment with steam. However, it has been ascertained that even if the odor forming components can initially be removed by such treatment, the odor, upon storage of the polymers or after the polymers have been mixed into cosmetic formulations, has a tendency to reappear.
EP-A-O 398 684 is concerned with the removal of such odor forming components. More particularly, the European patent application referred to is concerned with a purified polyether siloxane which has been treated in a closed system for a period of 24 hours with 10.sup.-4 n aqueous hydrochloric acid in the amount of up to 1000 ppm, calculated on polyether, at 60.degree. C. The product thus purified was then treated at reduced pressure with steam in order to remove the aldehydes and ketones which were formed during the acid treatment.
However, it was found disadvantageous that for the removal of the formed aldehydes and ketones, and calculated on the weight of the treated polyether siloxanes, about 11/2 as much steam had to be used. The procedure thus results in considerable amounts of acidic condensates of obnoxious odors which are difficult to dispose of.
An additional disadvantage of the acidic treatment referred to resides in the fact that if the polyether siloxane should contain residual SiH groups, oftentimes the formation of gel particles can be observed. These gel particles are difficult to remove by filtration.
Another known procedure for deodorizing polyoxyalkylene polysiloxane mixed block polymers is disclosed in U.S. Pat. No. 4,515,979. In accordance with the procedure there disclosed, phytic acid is added to the mixed block polymers during or after their preparation. As stated in the patent, the phytic acid used in the procedure referred to is a hexaphosphate ester compound of myoinositol represented by the molecular formula C.sub.6 H.sub.18 O.sub.24 P.sub.6 and is a compound which is known as a nontoxic, natural product occurring in abundance in corn, seeds, and the like in the plant kingdom. This product is not suitable for use on an industrial scale--one reason being the high cost of the product.